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Model A1418 / Late 2013 / 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7 Processor

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iMac suddenly won't turn on, no illumination LED#1. Likely problem?

Hi all.

SMC reset didn’t help. Imac was working fine then suddenly one day no sign of life. LED #1 doesn’t even turn on. I’m thinking a fuse or power-supply needs replacing?

Visual inspection everything looks fine. Any ideas? What is the most likely scenario here?

Thanks :)

Answered! View the answer I have this problem too

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If the onboard diagnostic LED #1 is out that implies the power supply is gone

Here's a breakdown of the onboard diagnostic LED's:

  • LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.
  • LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.
  • LED 3 - Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.
  • LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

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thanks, any likely / typical failure points on powerboard or should i just replace it?


And if replacing the power supply, which I did, doesn’t make any of the LEDs come on?

Am I missing a common or known issue with this model where we get no signs of life at all?


Ouch! So both the power supply and the logic board got hit! I'm suspecting you got a power surge or lightening strike that damaged your system.

Make sure you have all of your peripheral devices on good surge suppressors (anything that directly attaches to your Mac system. I would strongly recommend getting a UPS for your system or at least a surge suppressor.

To put this into perspective: I have three UPS's and four suppressors just for my home! I live in the city and my power is not very good. Between the sags, clipping, surges and low/over voltage its BAD! My largest support customer needed UPS's for all their systems!

Here's the needed part iMac Intel 21.5" EMC 2638 2.7GHz i5-4570R Logic Board and the guide iMac Intel 21.5" EMC 2638 Logic Board Replacement


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@danj - I saw this post while searching for answers to my problem. I tried upgrading memory on a late 2013 imac 21.5. you had commented on my original post. however, I saw this post with the LED information. the problem was no light on screen, getting the tada sound.

When I power up, the first 3 LED's are on solid. number 4 LED is not on.

What are my options and your best guess as to the problem.

thanks frank

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Becareful! The #4 LED won't be lit without the connection to the display. So if you haven't connected the display that is the correct action. You need a special cable extension set to have the display connected to have it set aside to work on the system.

If you are not getting an image on the screen you'll need to figure out if the issue is the power or date cable is not properly connected (or bad) I would take a flashlight held against the display to see if there is a faint image or see if in a darkened room your system has a glow.


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